1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device having a seal pattern preventing electrolytic corrosion and a method of fabricating the same.
2. Discussion of the Related Art
Generally, a Braun tube, also known as a cathode ray tube (CRT), has been most widely used as a display device because it can easily realize colors and has a fast operation speed. Therefore, the Braun tube has been a major display device for a TV monitor and a computer monitor.
However, the Braun tube (CRT) consumes too much power and has a large volume due to its structural limitation of maintaining a space between an electron gun and a screen. In addition, the Braun tube is too heavy to be portable. In order to resolve such problems or disadvantages of the Braun tube (CRT), various display devices have been developed, such as a TFT-LCD panel, which is currently in practical use.
The TFT-LCD panel can be fabricated thin for ultra-thin display devices, such as wall-mountable television sets. Additionally, the TFT-LCD panel has light weight and consumes considerably less power than that of the Braun tube (CRT). Thus, the TFT-LCD panel can be applied to a display screen of a notebook computer, which can be operated by a battery. As a result, the TFT-LCD panel is considered to be the next generation display device.
A fabrication of the TFT-LCD panel for a liquid crystal display device includes a TFT array process for forming switches applying pixel unit signals, a color filter process for forming a color filter array for realizing colors, and a liquid crystal cell process for forming unit liquid crystal cells driven by signals by adding a driving circuit to the completed TFT and color filter substrates.
The liquid crystal cell process will be described as follows. An alignment material is coated on the completed TFT and color filter substrates. A rubbing process is then carried out on the coated alignment material to provide liquid crystal molecules with uniform directions. Then, a cell gap forming process is carried out to maintain a space between the two substrates. Subsequently, an assembly process for bonding the two substrates to each other and a cell cutting process for cutting the bonded substrates by a cell unit are carried out. Thereafter, liquid crystals are injected in the unit cell, and polarizing plates are attached to both sides of the unit cell to complete the liquid crystal cell process.
The cell cutting process will now be described in detail.
The cell cutting process is to cut and separate the substrates to cell units after the bonding process. In a conventional TN mode, the cutting process by cell unit is carried out after liquid crystals are injected in a plurality of the cells. However, as a cell increases in size, liquid crystals are injected after the unit cell cutting process.
The cell cutting process includes a scribing process for forming a cutting line on a glass substrate using a diamond pen having a hardness greater than that of glass, and a breaking process for cutting the glass by applying external pressure.
A liquid crystal display device according to the related art is explained with reference to the accompanying drawings as follows.
FIG. 1 illustrates a schematic view of a TFT substrate for a liquid crystal display device according to a related art.
Referring to FIG. 1, gate and data lines 21 and 22 are formed on a first substrate 20 to vertically cross one another. Gate and data pads 24 and 25 are formed at the ends of the gate and data lines 21 and 22, respectively.
A thin film transistor 26 acting as a switching device is formed at each pixel area defined by the crossing point of the gate and data lines 21 and 22. A plurality of the pixel areas form active areas representing an image.
A seal pattern 30 is formed on the first substrate 20. The seal pattern 30 is formed on a liquid crystal margin area of a liquid crystal display panel.
In this case, the seal pattern 30 has a liquid crystal injection inlet for injecting liquid crystals in a later process.
Although it is not shown in the drawing, a black matrix, a color filter, a common electrode, and an alignment layer are formed on a second substrate, which is to be bonded and facing into the first substrate 20. The seal pattern 30 may be formed on the same area of the second substrate.
FIG. 2 illustrates a cross-sectional view of portion ‘X’ shown in FIG. 1.
Referring to FIG. 2, a gate pad pattern 24a formed of the same material as a gate line is formed on a first substrate 20. A passivation layer 35 is formed on the gate pad pattern 24a. 
Subsequently, the passivation layer 35 having a contact hole exposing a portion of the gate pad pattern 24a is formed on the entire surface of the first substrate 20. A pixel electrode 40 formed of indium tin oxide (ITO) is formed in the contact hole and on the passivation layer 35 adjacent to the contact hole. A seal pattern 30 is formed on the pixel electrode 40.
In this case, the contact hole is formed to improve adhesion between the seal pattern 30 and an organic layer, which is used as the passivation layer.
A black matrix 55 for shielding light is formed on the inner surface of a second substrate 60 facing into the first substrate 20. A common electrode 52 for simultaneously driving liquid crystals and the pixel electrode 40 is formed on the entire surface of the second substrate 60 including the black matrix 55.
FIG. 3 illustrates a cross-sectional view of portion ‘X’ shown in FIG. 1 to which a chip on glass (COG) method is applied according to the related art. Herein, the same elements of FIG. 2 are represented by the same numerals for simplicity.
Referring to FIG. 3, a gate pad pattern 24a formed of the same material as a gate line is formed on a first substrate 20. A passivation layer 35 is formed on the entire surface of the first substrate 20 including the gate pad pattern 24a. 
A black matrix 55 for shielding light is formed on the inner surface of a second substrate 60 facing into the first substrate 20. A common electrode 52 for simultaneously driving liquid crystals and the pixel electrode 40 is formed on the entire surface of the second substrate 60 including the black matrix 55. A seal pattern 30 is coated on one of the common electrode 52 and the pixel electrode 40.
However, the liquid crystal display device according to the related art has the following problem or disadvantage.
First of all, when the liquid crystal display device is driven for about 24 hours for a reliability test in high temperature and high humidity, after completion of the liquid crystal cell process, water or moisture may penetrate into the cell gap between the first and second substrates 20 and 60. This is because the pixel electrode 40, the common electrode 52, and the black matrix 55 formed of electrically conductive materials are formed outside the sealant 30. Therefore, the electrically conductive black matrix 55 and the gate pad pattern 24a may be deteriorated by electrolytic corrosion.